The “Five Protections” of high-voltage switchgear are designed to ensure personal and equipment safety. Specifically, they include: preventing accidental opening and closing of circuit breakers; preventing opening and closing of disconnectors under load; preventing the connection (or closing) of grounding wires (grounding switches) with power on; preventing power supply (i.e., closing circuit breakers) with grounding wires (grounding switches) under load; and preventing accidental entry into energized compartments. These functions are implemented through mechanical interlocks, electrical interlocks, electromagnetic locks, or computer interlocks.
Specific Contents of the “Five Protections”
1. Preventing Accidental Opening and Closing of Circuit Breakers
In high-voltage switchgear, measures must be taken to ensure that disconnectors or trolleys can only be operated when the circuit breaker is in the open position.
2. Preventing Opening and Closing of Disconnectors Under Load
This is one of the most dangerous misoperations of the five protections in high-voltage switchgear. Disconnectors cannot be operated when the circuit breaker or load switch is in the closed position.
3. Preventing Connection (or Closing) of Grounding Wires (grounding switches) Under Power
High-voltage equipment must not be connected to a grounding knife switch or grounding switch while it is energized. 4. Preventing Power from Being Resupplied (Closing the Circuit Breaker) with the Grounding Wire (Grounding Switch) Connected
Closing the circuit breaker can only be performed when the grounding switch is in the open position and the equipment is not energized.
5. Preventing Accidental Entry into Live Compartments
When equipment is energized, personnel must be prevented from accidentally entering the cabinet where potentials may exist.
Methods for Implementing the “Five Protections”
The “Five Protections” function can be implemented primarily in the following ways:
Mechanical Interlocking:
Mechanical devices provide mutual control between the circuit breaker, disconnector, grounding switch, and cabinet door. This design is simple and reliable.
Electrical Interlocking:
Interlocking is achieved by forming an electrical circuit using auxiliary contacts, relays, etc. This provides comprehensive functionality but carries the risk of contact failure. It is often used as a supplement to mechanical interlocking.
Electromagnetic Locking:
A simple and effective locking method, but it has certain limitations and is primarily used for cabinet door locking.
Microcomputer Interlocking:
This achieves comprehensive error prevention functionality through sophisticated software design, but is more expensive. Power indicator:
Serves only as a reminder to the user of the current device status and does not have a locking function.
Post time: Aug-27-2025
